Communication system for ultrahigh frequencies



Sept; 17, 1946.

L. J. WOLF COMMUNICATION SYSTEM FOR ULTRA HIGH FREQUENCY Filed April 22,. 1942 Amt/M 18.5 ozrz'cme 191/010 a fiMPuF/Ez 0A0 19- KC. flflPUf/E/B Imventor zwzerJimgr 8g attorney Patented Sept. 17, 1946 COMMUNICATION SYSTEM FOR ULTRA- HIGH FREQUENCIES Lester J. Wolf, Audubon, N. J assignor to Radio Corporation of America, a corporation of Delaware Application April 22, 1942, Serial No. 439,964

4 Claims. 1

This invention relates generally to radio transmitters and particularly to ultra-high frequency pulse transmitters modulated by voice or other signal frequencies.

It has long been recognized that considerable difficulty is experienced in generating ultra-high frequencies with transmitting tubes of high power rating. At present, high power telephone communication at frequencies of the order of 100 megacycles or higher is limited in the transmitter because of the difficulty in constructing vacuum tubes to handle large amounts of radio frequency power at these frequencies. This difficulty is seemingly inherent because of the interelectrode capacity and transit-time losses in conventional high power transmitting tubes. In a similar manner communication at these frequencies is limited in the receiver because of noise level due to static, ignition noises, etc., and to transit-time losses and reduced amplification. One solution to this problem is the use of a pulse transmitter in which extremely short pulses having high peak power are radiated from the transmitter. It is perfectly practical under these conditions to radiate a peak output of as much as 100 times the continuous power rating of a transmitting.

tube designed for operation at the frequencies previously mentioned.

Among the objects of the invention are to provide improved methods and means for generating and modulating ultra-high frequency pulses of radio frequency energy having peak power many times greater than the continuous power rating of the transmitting tubes. Another object is to provide an improved method and means for modulating ultra-high frequency pulses of radio frequency energy by controlling the blocking and unblocking of an oscillator circuit in response to modulation potentials. Another object is to provide improved means for blocking an oscillator circuit and unblocking the circuit through a leakage path through a modulator tube circuit.

The invention will be described by reference to the drawing of which Figure 1 is 'a schematic circuit diagram of one modification of the invention; Figure 2 is a graph showing the operating characteristics of the circuit; and Figure 3 is a block diagram of a receiver for signals from the system to be described. It should be understood that the invention will be adaptable to any standard transmitter circuits and that the circuit described and illustrated is merely one embodiment of the invention.

Referring to Fig. 1, a push-pull oscillator circuit utilizing tuned anode, grid, and cathode cir- 2 cuits, consisting of tuned transmission lines, is shown in combination with a modulator having a conventional input circuit. The oscillator tubes 2 are connected respectively to the tuned .resonant 7 lines 6 and l which are tunedby the shorting bar 8. The cathodes of the oscillator tubes l and 2 are connected respectively to the resonant lines 9 and [0 which are tuned by the shorting bar It. A capacitor 12 is connected between the shorting bars 8 and H. The shorting bar 8 is also connected to the cathode of the modulator tube l3.

,The grid circuit of the modulator I3 includes the secondary of a modulation transformer M and an adjustable source of grid potential 15. The primary of the modulation transformer M is supplied with modulating potential applied to the input terminals IS. The negative terminal of the high potential anode power supply is connected to the shorting bar I l.

In operation the modulator tube acts as a grid leak of very high resistance for the grid capacitor l 2 in the oscillator circuit. When the high anode voltage is applied to the oscillator tubes l and 2, they commence to oscillate very abruptly, and a high peak power radio frequency current is generated. The resultant high grid current in the oscillator circuit rapidly charges the small con-' denser l2, and the bias on the oscillator tubes rises to a blocking value within a few microseconds. The oscillator tubes l and. 2 will remain blocked until the condenser I2 can discharge through the leakage path provided by the anode circuit of the modulator tube l3.

The bias potential onthe grid of the modulator tube [3 is adjusted to the value which will provide an anode resistance of a predetermined value for pulsing the oscillator. circuit at any desired frequency. Modulation potential applied to the terminals I 6 of the modulation transformer I4 will vary the grid potential of the modulator l3, which in turn will vary the anode resistance of the modulator. Any change in the anode resistance of the modulator l3 will vary the discharge time of the capacitor I2 in the grid circuit of the oscillators l and 2. Variations of the discharge time of the capacitor I2 will vary the interval between successive pulses of radio frequency power in the oscillator circuit, and may possibly vary the shape of the individual pulses. The use of the extremely high anode voltage on the oscillators and modulator will also tend to reduce the transit-time losses in these circuits.

Fig. 2 shows the variation in time interval between successive radio time frequency pulses resulting from a variation in the resistance of the leakage path through the tube i3 for the capacitor l2.

Fig. 3 is a block diagram of a receiver which will provide satisfactory reception of the signals radiated from the transmitter of Fig. '1. The receiver may be of any conventional design such as a radio frequency amplifier 3| followed by a detector-A, V. C. circuit 32, and an audio amplifier 33 connected to a reproducer 34. The .automatic volume control circuit is shown connected to the radio frequency amplifier by the line 35, so as to bias off all but the peak portion of the received pulses as shown by the pulse peaks 22 above the dash line 2% in Fig. 2. The average noise level indicated by the curve 2| in Fig. 2 ordinarily will be considerably lower than the A. V. C. limiting value 20 and will, therefore, provide substantially noiseless reception. It should be understood that this limiting feature may be applied to any conventional radio receiver by this or other well known methods.

I claim as my invention:

1. A pulse transmitter including an oscillator having tuned anode and control electrode circuits coupled to provide oscillations, a capacitor in said control electrode circuit connected to effectively block said oscillations, a modulator having control electrode and anode circuits, means for applying modulating potentials to said modulator control electrode circuit to vary the resistance of said modulator anode circuit, and means connecting said modulator anode circuit between said oscili lator anode and control electrode circuits for varying the time intervals between pulses generated by said oscillator in accordance with said modulator anode circuit variations.

2. A pulse transmitter including a pair of oscillator tubes having push-pull tuned anode and control electrode circuits coupled to provide oscillations, a capacitor in said control electrode circuit connected to effectively block said oscillations, a modulator having control electrode and anode circuits, means for applying modulating potentials to said modulator control electrode circuit to vary the resistance of said modulator anode circuit, and means connecting said modulator anode circuit between aid oscillator anode and control electrode circuits for varying the time intervals between pulses generated by said oscillator in "accordance with said modulator'anode circuit variations.

3. A pulse transmitter including a pair of oscillator tubes having push-pull tuned anode,

control electrode and cathode circuits coupled to provide oscillations, a capacitor connected between said control electrode and said cathode circuits to effectively block said oscillator tubes, a modulator tube having a variable resistance anode circuit, means for varying said anode resistance of said modulator as a function of modulating potentials applied to said modulator,- and means connecting said modulator anode circuit between said oscillator anode and control electrode circuits for varying the time intervals between pulses generated by said oscillator in accordance with said modulator anode circuit variations.

4. Apparatus of the type described in claim 2 including variable means in said modulator circuit for adjusting said modulator anode circuit resistance.

LESTER J. WOLF. 

